Our British Patent 2171218B discloses and claims the idea of deploying a cable in a pipeline using the drag of a flowing liquid. A near neutrally buoyant cable is deployed into the pressurised fluid-filled pipeline which has flow. Drag due to friction of the fluid over the cable allows deployment of the cable over long distances for example 2-10 kilometers. A drogue is employed at the end of the cable, its function being to guide and provide extra pulling force created by the additional drag of the fluid on the drogue. The cable is deployed at less than the flow rate in the pipe in order to maintain sufficient drag to overcome friction due to cable touching the pipe wall and capstan effects around bends in the pipe, gravitational effects and pressure difference forces.
As the cable is being deployed it is not always easy to determine if deployment is proceeding satisfactorily; for example there may be an obstruction in the pipeline, the drogue may become snagged on the pipeline wall where it is perhaps corroded, the drogue may not inflate properly after insertion through the side wall entry valve or the liquid flow rate may change or even cease altogether.
If any of these problems arise during deployment they may prevent satisfactory deployment and/or damage the cable if remedial steps are not quickly taken.
It is an object of the present invention to monitor the deployment of a cable and to enable problems such as those described above to be quickly determined.